This invention relates generally to extrusion dies, and more particularly, to methods and systems for designing profile extrusion capping dies.
Profile extrusions are made by heating, for example, a thermoplastic resin in the barrel of an extruder and forcing it through a profile extrusion die that shapes it into a continuous two-dimensional shaped part. Typically, such parts are made from a single thermoplastic. However, where one or more surfaces of a part require greater strength, or greater durability such as weatherability or protection from ultraviolet light degradation, or a different color, etc., a second different plastic resin is often applied onto the one or more surfaces of the part using a capping die.
Typically, a capping die is disposed on the downstream side of a profile die during the extrusion process. The capping resin is fed in through a runner or manifold and a land formed by the capping die to apply a thin layer or capping to the desired surface of the part as it exits the extruder. Desirably, the capping die is sized and configured to provide a uniform velocity to the capping resin at an outlet of the land formed by the capping die so that a capping having a uniform thickness is applied to the part.
A capping die often has complicated cavity geometries to achieve a uniform capping thickness. The design and fabrication of a capping die requires many cutting trials and iterations. For example, an initial capping die is designed and fabricated, and then tested on a production line extruder to determine if the capping die produces the desired uniform capping. If the capping is not uniform, then the die must be re-cut.
This iterative process requires skilled designers and machinists and is labor and time intensive. In addition, modification to the capping die, is required if the dimensions of the profile die are changed or if a new plastic capping resin having different material properties is used in the extrusion process.